Novel tetrahydropyrimidines

ABSTRACT

Novel 1, 2, 3, 4-tetrahydropyrimidine-2,4-diones of the formula   WHEREIN R1 is selected from the group consisting of lower alkyl of one to seven carbon atoms and phenyl, R2 is selected from the group consisting of hydrogen, chlorine, bromine and lower alkyl of one to seven carbon atoms and n is 3 or 4 which have herbicidal activity and their preparation and intermediates therefor.

United States Patent [1 1 Bertin et al.

' [111 3,811,863 [451 May 21, 1974 NOVEL TETRAHYDROPYRIMIDINES [75] Inventors: Daniel BertimJacques Perronnet; Andre Teche, all of Paris, France [73] Assignee: Roussel-UCLAF, Paris, France 22 Filed: Oct. 19, 1972 [21] Appl. No.2 298,859

- Related [15. Application Data [62] Division of Ser. No. 126,865, March 22, 1971, Pat.

[30] Foreign Application Priority Data Mar. 26, 1970 France 70.10906 Jan. 28, 1971 France 71.02829 52 U.s.ci. 41.11/92. [51] Int. Cl A0ln 9/22 [58] Field of Search ..71/92 [56] References Cited UNITED STATES PATENTS 3,374,083 3/1968 Loux 71/92 3,466,285 /1969 LouX..

2/1966 Loux....;.

Primary ExaminerLewis Gotts Assistant Examiner-Catherine L. Mills Attorney, Agent, or Firm-Hammond & Littell 5 7] ABSTRACT wherein R is selected from the group consisting of lower alkyl of one to seven carbon atoms and phenyl, R is selected from the group consisting of hydrogen,

chlorine, bromine and lower alkyl of one to seven carbon atoms and n is 3 or 4 which have herbicidal activ ity and their preparationand intermediates therefor.

13,Claims, No Drawings .NOVEL TETRAHYDROPYRIMIDINES PRIOR APPLICATION This application is a division of our copending, commonly assigned application Ser. No. 126,865 filed Mar. 22, 1-971, now US. Pat. No. 3,732,228.

STATE OF THE ART Certain tetrahydropyrimidines are known to possess herbicidal activity. For example, 3-sec.butyl-5-bromo- 6-methyll ,2,3,4-tetrahydropyrimidine-2,4-dione, sold under the name bromacile, is used for eradicating I weeds in orchards of adult peach trees. Unfortunately,

these compounds cannot be-generally used except as total herbicides as their activity is not selective.

OBJECTS OF THE INVENTION- It is an object of the invention to provide the novel l,2,3,4-tetrahydropyrimidine-2,4-diones of formula I.

It is another object of the invention to provide a novel process for the preparation of the compounds of formula I and to provide. the novel intermediates formed in said process.

It is an object of the invention to provide novel herbicidal compositions and to provide a novel method of killing undesiredplants.

The novel process of the invention for the preparation of the tetrahydropyrimidines of formula I comprises condensing an alkyl B-amino-acrylate of the formula Alk-O O C II wherein R, and R have the above definitions and Alk is lower alkyl of one to seven carbon atoms with an isocyanate selected from the group consisting of 2- tetrahydropyranyl isocyanate and Z-tetrahydrofuranyl These and other objects and advantages of the inven- 4 tion will become obvious from the following detailed description.

THEINVENTION d The novel l,2,3,4-tetrahydropyropyrimidine-2,4 diones of the invention have the formula wherein R is selected from the group consisting of isocyanate in the presence of'a basic agent to form an alkyl B-(Nf-2-tetrahydroheterocylic ureido)-acrylate of the formula e=o o gem), Alk-00C Nrr-b-NH-o wherein .R,, R Alk and n have the above definitions and cyclizing the latter in the presence of a basic agent to fonn the corresponding compound of formula 1.

Preferably the basic condensation agent is a tertiary amine such as trimethylamine, triethylamine, pyridine, N-methyl-piperidine, N-methyl-pyrrolidine' or quinoline. The basic cyclization agent is preferably an alkali metal lower alcoholate such-as sodium methylate or sodium ethylate. The cyclization is preferably effected in an organic solvent such as an alcohol, e.g., ethanol.

' The starting alkyl B amino acrylates of formula II can be prepared from a compound of the formula 0 RI 0.... R,-l J- bHd0Au rv wherein R R and Alk have the-above definitions by a process analogous to that described by Genvresse (Ann. de Chim., Vol. 24, p. 64). Z-tetrahydrop'yranyl isocyanate may be prepared by the process described in French Pat. No. 1,425,137 and2-tetrahydrofuranyl isocyanate may be prepared by reacting 2-chlorotetahydrofuran with acetonitrile.

The process of the invention comprises two stages, the condensation and cyclization. The intermediate resulting from the condensation step may be recovered and purified and then cyclized or the cyclization may be effected in the reaction mixture resulting from the condensation.

3-(2 '-tetrahydrofuran yl )-6- methyl-1 ,2,3 ,4-

B-ureido-ac-rylate of the formula In a variationof the process of the invention, the compounds of formulaIll' may be prepared by condensing in the presence of a dehydration agent an alkyl Amoco v wherein R R and Alk have the above definitions with dihydropyran or dihydrofuran to obtain the corresponding compound of formula III; The preferred dehydration agent is p-toluenesulfonic acid and the reaction is effected in the presence of an organic solvent such as benzene, toluene, xylene or tetrahydrofuran. The compound of formula V can be prepared by condensing urea with a compound of formula IV.

To obtain a compound of formula 1 wherein R is chlorine or bromine, the corresponding compound of formula I where R is hydrogen is reacted with a'halogenation agent. Suitable halogenation agents are sulfuryl chloride where R; is to be chlorine and bromine or N-bromo-succinimide when R; is to be bromine. I

The compounds of formula 1 present little or no phytotoxic activity against certain valuable plants such as cotton and can therefore be used to kill parasitic weeds in fields of the useful plants. The said compounds have preand post-emergence herbicidal activity as can be seen from tests against large botanical families such as foxtail grass, chrysanthemum, flax, mustard, oats, wheat, corn, clover and beets.

The novel herbicidal compositions of the invention are comprised of at least one compound of formula I and an inert carrier. The compositions may be in the form of powders, granules and suspensions, emulsions or solutions containing the active ingredients, for example a mixture with a vehicle and/or an anionic, cationic or non-ionic surface active agent to insure a uniform dispersion of the substances in the composition. The vehicle may be a liquid such as water, alcohol, hydrocarbons or other organic solvents, a mineral, animal or vegetable oil or a powder such as talc, kieselguhr, silicates or clay.

The solid compositions in the form of a dusting powder, wettable powder or granules may be prepared by grinding the active compound with an inert solid or by impregnation of a solid support with a solution of the active ingredient in a solvent and evaporating the solvent. The compositions may contain other active agents such as other pesticides, herbicides, and/or fungicides, biocides, insecticides, etc., and other compounds influencing the growth of the plants.

The novel process of killing weeds comprises contacting weeds with a herbicidal amount of at least one compound of formula 1 either before or after emergence of the weeds. The usual useful amount of the active compound is 0.2 to 40 kg/ha and preferably 0.6 to 5.0 kg/ ha. The exact amount will vary as a function of treated vegetation, the nature of terrain, atmospheric conditions and state of growth.

In the following examples here are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

EXAMPLE 1 PREPARATION OF 3-(2-tetrahydropyranyl)-5,6- dimethyl-l ,2,3,4-tetrahydropyrimidine-2,4rdione A mixture of 42.9 g. of ethyl 2-methyl-3-aminocrotonate in 600 cc of toluene, 52.5 g. of 2- tetrahydropyranyl isocyanate and 42 cc of triethylamine was refluxed for 17 hours and was then cooled to 20C. The mixture was introduced into a solution of 60 g of sodium methylate in 300 cc of ethanol and the mixture was progressively heated to reflux and held there for 30 minutes. After cooling to 20C, 300 cc of water were added thereto and the organic phase was decanted off. The aqueous phase was extracted with ether and then the pH was adjusted to 4 by the addition of acetic acid. The precipitate formed was recovered by Analysis C H N 0 molecular weight 224.26

Calculated C 58.9 H 7.19 %N 12.50 Found 58.8 7.2 12.60

- As far as is known, this compound is not described in the literature. I

EXAMPLE II Using the procedure of Example I, ethyl 2-chloro-3- amino-crotonate and Z-tetrahydrofuranyl-isocyanate were reacted to form 3-(2-tetrahydrofuranyl)-5- chloro-6-methyll ,2,3,4-tetrahydropyrimidine-2,4- dione melting at 200C.

As far as is known, this compound is not described in the literature.

The Z-tetrahydrofuranyl-isocyanate is prepared as follows:

A mixture of 75 g of 2-chloro-tetrahydrofuran [prepared by method of Normant, C. R., Vol. 228 (1949), p. 102], 150 cc of anhydrous acetonitrile, 150 cc of anhydrous benzene and g of sodium cyanate was held at a temperature of 3538C. for 2% hours and then was refluxed for 10 minutes and then was cooled. The insoluble precipitate was removed by vacuum filtration and the solvents were evaporated off under reduced pressure and rectification gave 40 g of 2- tetrahydrofiiranyl isocyanate having a melting point of 60C at 35 mm Hg.

As far as is known, this compound is not described in the literature.

EXAMPLE lll PREPARATlON OF 3-(2-tetrahydropyranyl)-6- methyl-1,2,3,4-tetrahydropyrimidine-2,4-dione A mixture of 30 g of ethyl 3-amino-crotonate, cc of anhydrous toluene, 15 g of triethylamine and 30 g of 2 -tetrahydropyranyl isocyanate was refluxed under a nitrogen atmosphere for 2 hours and the resulting solution was cooled to room temperature and then was added to 150 cc of ethanol and 30 g of sodium methylate. The reaction mixture was refluxed for l-hour and the solution was then concentrated to about cc. After addition to water, the mixture was washed with methylene chloride. The resulting aqueous phase was concentrated, acidified to a pH of 2 by the addition of hydrochloric acid and was then vacuum filtered to obtain 26g of 3-(2-tetrahydropyranyl)-6-methyl-1,2,3,4- tetrahydropyrimidine-Z,4-dione melting-at 224C.

As far as is known, this compound is not described in the literature.

EXAMPLE lV PREPARATION OF 3-( 2 -tetrahydropyranyl )-5- chloro-6-methyl-l ,2,3 ,4-tetrahydropyrimidine-2,4- dione STEP A: Ethyl a-chloro-B-ureido-crotonate A mixture of g of ethyl a-chloro-acetylacetate [prepared by method of Allihn, Ben, Vol 1 l (1878), p.

- 5'67], 60 g of urea and a few cc of pure hydrochloric acid was heated with agitation at 50-5 5C for 16 hours at a pressure of 80 mm Hg. After cooling the reaction mixture, theprecipitate was recovered by vacuum filtration and washed with ether and then water to obtain 37 g of ethyl a-chloro-B-ureido crotonate melting at l- 81C.

As far as is known, this compound is not described in the literature. 7 STEP B: Ethyl B-(N'2-tetrahydropyrany1-ureido)-achloro-crotonate A mixture of 25 g of ethyl a-chloro-B-ureidocrotonate, 12.5 g of dihydropyran and 2 g of p-toluenesulfonic acid in 650 cc of tetrahydrofuran was refluxed with agitation for 4 hours and after cooling, 500 cc of ethyl acetate were added thereto. The mixture was washed with water, dried over magnesium sulfate and then evaporated to dryness under reduced pressure. The oily residue was crystallized from isopropyl ether to obtain 10 g of ethyl B-(N'-2tetrahydropyranylureido) a-chloro-crotonate melting at 107C.

As far-as is known, this compound is not described in the literature. STEP C: 3-(2'-tetrahydropyran'y1)-5-ch1oro-6-methy1- l ,2, 3,4-tetrahydropyrimidine-2,4-dione 25 g of ethyl /3-(N'-2-tetrahydropyranyl-ureido) achloro-crotonate wereadded all at once to a solution of 25 g of sodium methylate in 250 cc of ethanol and the mixture was refluxed for 30 minutes and was then evaporated to dryness under reduced pressure. The oil formed was dissolved in water and the solution was acidifiedby the addition of pure hydrochloric acid. The precipitate formed was recovered by vacuum filtration to obtain g of 3-(2'-tetrahydropyrany1)-5-chloro-6- methyl-1 ,2,3,4-tetrahydropyrimidine-2,4-dione melting at 225C. A sample of the product after crystallization from ethyl acetate was analyzed as follows:

Analysis C H Cl N 0 molecular weight 244.68

Calculated Found As far as is known, this compound is not described in the literature.

. EXAMPLE V 3-( 2'-tetrahydropyrany1)-5 -ch1oro-6 methy1-l ,2,3,4- tetrahydropyrimidine-2,4-dione 1.4 cc of sulfuryl chloride was added dropwise to a solution of 3.5 g of 3-(2'-tetrahydropyrany1)-6-methy1- 1,2,3,4-tetrahydropyrimidine-2,4-dione (of Example 111) in cc of chloroform cooled to 0C and after stirring for 30 minutes at 0C, 20 cc of chloroform were EXAMPLE VI PREPARATION OF 3-(2-tetrahydropyrany1)-5- bromo-6-methyl-l ,2,3,4-tetrahydropyrimidine-2,4- dione 24 g of 3-(2'-tetrahydropyrany1)-6-methy1-1,2,3,4- tetrahydropyrimidine-Z,4-dione were added to a solution containing 25g of N-bromosuccinimide and 250 cc of carbon tetrachloride and the solution was refluxed for minutes. After cooling to room temperature, 250 cc of methylene chloride were added to the mixture which was then washed with water, dried over sodium Analysis C H Br N 0 molecular weight 289,14

Calculated Found As far as is known, this compound is not described in the literature.

EXAMPLE vu PREPARATION OF 3-(2'-tetrahydrofuranyl)-5- bromo-6-methyl-l ,2,3,4 tetrahydropyrimidine-Z,4- dione STEP A: 3-(2-.tetrahydrofuranyl)-6-methyl-1,2,3,4- tetrahydropyrimidine-2,4-dione 46 g of 2-tetrahydrofuranyl isocyanate were added under nitrogen to a solution containing 46 g of ethyl 3- amino-crotonate, 12.8 g of triethylamine and 90 cc of anhydrous toluene and the mixture was refluxed for 90 minutes and then was cooled to room temperature. 35.5 g of sodium methylate and 180 cc of ethanol were added to the reaction mixture and the resulting solution was refluxed for 1 hour and then evaporated to dryness under reduced pressure. The yellow oil residue was dissolved in 200 cc of water and the solution was washed with 40 cc of methylenechloride and evaporated to dryness under reduced pressure. The residue was dissolved in cc of water and the solution was made slightly acidic by addition of concentrated hydrochloric acid. The resulting precipitate was recovered by vacuum filtration and was dissolved in methylene chloride. The organic solution was dried over sodium sulfate, filtered and evaporated to dryness under reduced pressure. The residue was empasted with ethyl ether to obtain 25 g of 3 -(2-tetrahydrofuranyl)-6-methyl- 1 ,2,3,4- tetrahydropyrimidine-2,4-dione melting at 202C.

Analysis C,H,,N,0,' molecular weight 196.19

Calculated Found Analysis C, H Br N molecular weight 275.08

Calculated %H 4.03 Found 4.1

As far as is known this compound is not described in the literature.

EXAMPLE V111 0.57 cc of sulfuryl chloride were added to a solution of 1.2 g of 3-(2'-tetrahydrofuranyl)-6-methyl-1,2,3,4- tetrahydropyrimidine-2,4-dione in 20 cc of chloroform and the mixture was stirred for 1 hour at 0C. The resulting suspension was made basic by the addition of caustic potash and 20 cc of water were added thereto. The solution was decanted and the aqueous phase was made acidiic by addition of concentrated hydrochloric acid. The white precipitate was recovered by vacuum filtration and then was dissolved in chloroform. The solution was dried over sodium sulfate, filtered and evaporated to dryness under reducedpressure to obtain 1 g of white product which was crystallized from ethanol to obtain 0.5 g of 3 (2-tetrahydrofuranyl)-5-chloro-6- methyl-1,2,3,4-tetrahydropyrimidine-2,4-dione melting at 200C. The product was identical to that of Example 11.

Analysis C, H CI N 0 molecular weight 230.63

PREPARATION OF 3-(2-tetrahydropyranyl)-6- phenyl- 1 ,2',3,4-tetrahydropyrimidine-2,4-dione 'STEP A: Ethyl ,B-(N'-2-tetrahydropyranyl-ureido)- acrylate 71 g of ethyl ,B-phenyl-B-amino-acrylate [prepared by method of Lukes et al., C. A., Vol. 54 (1960), p.

I 1 1984c] and 3 cc of triethylamine were added to 200 cc of toluene. and then 66.9 g of 2'-tetrahydropryanyl isocyanate and 100 cc of anhydrous toluene were added to the reaction mixture. The mixture was refluxed for 12 hours and the toluene was distilled off under reduced pressure. The yellow oil residue was taken up in 100 cc of absolute ethanol to obtain 216.5 g of an alcoholic solution of ethyl ,B-(N'-2- tetrahydropyranyl-ureido)-acrylate.

As far as is known, this compound is not described in the literature. STEP B: tetrahydropyrimidine-2,4-dione A mixture of 144 g of the alcoholic solution of Step A and 15 g of sodium ethylate in 150 cc of absolute ethanol was refluxed for 12 hours and then evaporated to dryness under reduced pressure. The solid residue was taken up in 250 cc of ether and the solution was filtered 3-(2-tetrahydropyranyl--phenyl-1,2,3,4-

and the solid was washed twice with 50cc of ether. The solid obtained was dissolved in 1 liter of water and the solution was adjusted to a pH of 4 by addition of concentrated hydrochloric acid. The precipitate was recovered by vacuum filtration and was empasted three times with isopropyl ether and vacuum filtered to obtain a white product. The said product was crystallized from 18 volumes of isopropanol to obtain 17 g of 3-(2- tetrahydropyranyl) 6-phenyl-1,2,3,4-tetrahydropyrimidine-2,4-dione melting at 235C. 1

Analysis C H MO Molecular weight 272.30

Calculated %H 5.92 Found 6.1

As far as is known, this compound is not described in the literature.

tetrahydropyrimidine-2,4-dione of Example IX were added to 30 cc of chloroform and then 1.3 cc of sulfuryl chloride and 20 cc of chloroform were added to the mixture at 0C. The reaction mixture was stirred at 0C for 45 minutes, and the resulting solution was added to an aqueous sodium carbonate solution. The decanted chloroform solution was washed with cc of water, was dried over sodium sulfate, filtered and evaporated to dryness under reduced pressure. The residue was taken up in isopropyl ether and the product obtained by filtration thereof was crystallized from isopropyl alcohol and then from ethyl acetate to obtain 1.1 g of 3- (2-tetrahydropyranyl)-5-chloro-6-phenyl-1,2,3,4-

tetrahydropyrimidine-2,4-dione melting at l94-196C.

Analysis C H Cl N103 molecular weight 306.751

Calculated %C 58.73 %H 4.13 %CI 11.56 %N 9.13 Found 58.8 5.1 11.4 8.8

As far as is known, this compound is not described in the literature.

EXAMPLE Xl 9 10 Tables III and IV show the results of preand post Analyse CwHwB' molecular Weigh! 351-21 emergence tests with 3-(2-tetrahydropyrannyl)-5- Calculated %c 51.30 %1-1 4.30 %Br 22.76 %N 7.97 tetrahydmpynmldme'zv4 Found 51.4 4.1 22.3 7.8 d1one (compound B) As far as 1s known, this compound 1s not descr1bed 1n TABLE PRE EMERGENCE the literature." g g I-IERBICIDAL ACTIVITY Oats, clover, beets, wheat, corn flax, mustard, chry- 3 100 69 61 santhemum foxtail grass were cultivated in a double 10 8 8 bottom box (23 X 14 X 4 cm) with wetting from underfoxtail grass 100 100 100 88 neath. 20 seeds of each species were placed in rows 3 gfg :88 :88 g8 :88 cm apart in one box and four repetitions were used for Flax 100 100 100 75 each concentration. The following culture conditions {g8 :88 :88 '22 were observed: temperature of 20C i 2, about 60 per- 15 cent humidity, fluorescent tube light (light of. day brilliant white) for 16 hours each day. The soil mixture used was 10 volumes of river sand, 10 volumes of ma TABLE IV POST EMERGENCE ble soil and 2 volumes of peat.

For the pre-emergence test, the treatment was ef-' 20 Kg 5 fected 24 hours after the seeding and the first wetting o 100 100 I00 100 was effected by aspersion culture to entrain a part of /heat 3? 2 v 45 the product to the level of theseeds. For the post emer- 83 grass 00 100 3g 8 gence test, the treatmentwas effected after 21 days of Beets 100 100 100 100 growth with the above ground parts. 2 gg {8g :88 {8g :88

In both cases, the test compounds were applied in I Mustard 100 100 100 100 standard compositions with a micro-pulveriser at doses 100 corresponding to 5, 2.5, 1.25 and 0.62 kg/ha at a dilution corresponding to 560 liters per ha. The test controls were subjected to the same treatment without the :12:32. a gigggggg g; g fi gg fifigfiz pgg l gs z ggi' f i g g fg gg gzi g gz ing from the spirit or scope thereof and it is to be un- I g e p y p derstood that the invention is to be limited only as deemergence test and 15 days after treatment 1n the post- Y fined 1n the appended cla1ms. emergence test and the results were expressed as perr we claim, ce-ntage of a mlP Yfi mW 219 1. A herbicidal composition comprising on herbicidwelght of gg j z i gfig' of ally effective amount of at least one compound of the X 100 formula weight of control plants The following tables report the results with 3-(2'- H tetrahydropyranyl)-5-chloro-6-methyl-1,2,3,4- 1 tetrahydropryimidine-2,4-dione (compound A) and mm) the commercial preemergence herbicide, Atrazine, (2- R l t I g chloro-4-ethylamino-6-isopropylamino-l ,3,5-triazine) T or the post emergence herbicide, Linuron [N'-(3,4- C 0 dichlorophenyl)-N-methoxy-N-methyl-urea]. g

" TABLE I PRE-EMERGENCE Compound A Atrazine IVIA Kg/ha 5.0 2.5 1.25 0.62 5.0 2.5 1.25 0.62 Oats 65.0 45.0 Y 100 Beets I00 I00 Wheat 100 78.0 55.0 22.0 67.0 64.0 50.0 50.0 Chrysanthemum I00 I00 Flax 100 94.0 84.0 100 Corn 65.0 1 45.0 17.0 1.1.0 0 0 0 0 Mustard I00 I00 Clover I00 [00 Foxtail grass I00 7100 TABLE 11 Po'sT' EMERGENCE Compound A Linuron Kg MA/ha 5.0 2.5 1.25 0.62 5.0 2.5 1.25 08.62 100 l B eis I00 I00 Wheat 100 100 55.0 00.0 Chrysanthemum I00 I00 flux 100 I00 corn 30.0 31.0 20.0 15.0 65.0 30.0 20.0 5.0 mustard I00 I00 clover I00 I00 foxtail grass 100. 85.0 I00 40.0 60.0

wherein R, is selected from the group consisting of lower alkyl of one to seven carbon atoms and phenyl, R is selected from the group consisting of hydrogen, chlorine, bromine and lower alkyl of one to seven carbon atoms and n is 3 or 4 and an inert carrier.

2. A method for the post-emergence killing of weeds which comprises contacting weeds with a herbicidal amount of at one compound of the formula wherein R,- is selected from the group consisting of wherein R is selected from the group consisting of lower alkyl of one to seven carbon atoms and phenyl, R is selected from the group consisting of hydrogen, chlorine, bromine and lower alkyl of one to seven carbon atoms and n is 3 or 4.

4. A method of claim 3 which is 3-(2'- tetrahydropyranyl)-5-chloro-6-methyl-l ,2,3 ,4-tetrahy- I dropyrimidine-2,4-dione.

5. A method of claim 3 which is 3-(2- tetrahydropyranyl)-5,6-dimethyll ,2,3 ,4-tetrahydropyrimidine-2,4-dione.

6. A method of claim 3 which is 3-(2- tetrahydrofuranyl )-5-chloro-6-methyll ,2,3,4-tetrahydropyrimidine-2,4-dione.

7. A method of claim 3 which is 3-(2- tetrahydropyranyl)-6-methyll ,2,3,4-tetrahydropyrimidine-2,4-dione.

8. A method of claim 3 which is 3-(2'- tetrahydropyranyl)5-bromo-6-methyl-l ,2,3,4-tetrahydropyrimidine-2,4-dione.

9. A method of claim 3 which is 3-(2'- tetrahydrofuranyl )-5-bromo-6-methyll ,2,3 ,4-tetrahydropyrimidine-2,4-dione.

10. A method of claim 3 which is 3-(2'- tetrahydrofuranyl )-6-methyll ,2,3 ,-4-tetrahydropyrimidine-2,4-dione.

11. A method of claim 3 which is, 3-(2'- tetrahydropyranyl )-6-phenyll ,2,3 ,4-tetrahydropyrimidine-2,4-dione.

12. A method of claim 3 which is 3-(2- tetrahydropyranyl )-5-chloro-6-phenyll ,2,3 ,4-tetrahydropyrimidine-2,4-dione.

13. A method of claim 3 which is 3-(2'- tetrahydropyranyl )-5-bromo-6-phenyll ,2,3 ,4-tetrahydropyrimidine-2,4-dione. 

2. A method for the post-emergence killing of weeds which comprises contacting weeds with a herbicidal amount of at one compound of the formula
 3. A pre-emergence method of killing weeds which comprises incorporating into soil before the emergence of weeds a herbicidally effective amount of at least one compound of
 4. A method of claim 3 which is 3-(2''-tetrahydropyranyl)-5-chloro-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4 -dione.
 5. A method of claim 3 which is 3-(2''-tetrahydropyranyl)-5,6-dimethyl-1,2,3,4-tetrahydropyrimidine-2,4 -dione.
 6. A method of claim 3 which is 3-(2''-tetrahydrofuranyl)-5-chloro-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4 -dione.
 7. A method of claim 3 which is 3-(2''-tetrahydropyranyl)-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4-dione.
 8. A method of claim 3 which is 3-(2''-tetrahydropyranyl)5-bromo-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4 -dione.
 9. A method of claim 3 which is 3-(2''-tetrahydrofuranyl)-5-bromo-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4 -dione.
 10. A method of claim 3 which is 3-(2''-tetrahydrofuranyl)-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4-dione.
 11. A method of claim 3 which is 3-(2''-tetrahydropyranyl)-6-phenyl-1,2,3,4-tetrahydropyrimidine-2,4-dione.
 12. A method of claim 3 which is 3-(2''-tetrahydropyranyl)-5-chloro-6-phenyl-1,2,3,4-tetrahydropyrimidine-2,4 -dione.
 13. A method of claim 3 which is 3-(2''-tetrahydropyranyl)-5-bromo-6-phenyl-1,2,3,4-tetrahydropyrimidine-2,4 -dione. 